Integrated handover authentication technology for a next generation network (NGN) environment to which wire-less access technology and mobile IP based mobility control technology are applied is provided. In a method of operating a mobile terminal MN in order to perform the integrated handover authentication in the NGN environment including an access router PAR, a target router NAR, and an authentication(AAA) server. First, a handover authentication key HKNAR which is shared by the mobile terminal and the target router and protects a fast binding update (FBU) message between the mobile terminal and the target router is generated. Then, an authentication request message AAuthReq generated using the handover authentication key HKNAR is transmitted. Thereafter, an authentication success message AAuthResp is received in response to the authentication request message AAuthReq. Accordingly, hierarchical handover can be performed according to the localization of the mobility of the mobile terminal, thereby minimizing the overhead of the authentication (AAA) server.